MONDAY, July 29 (HealthDay News) -- Bipolar disorder develops differently in obese people and among those who binge eat, a new study finds.

Up to 4 percent of Americans have bipolar disorder, a serious mental illness that causes extreme mood swings. Just less than 10 percent of people with bipolar disorder are binge eaters, which the authors of the new study said is a higher rate than in the general population.

This study found that bipolar patients who binge eat are more likely to have other mental health problems, such as suicidal thoughts, psychosis, anxiety disorders and substance abuse.

More women than men with bipolar disorder were binge eaters or obese, according to the study, which was published online recently in the Journal of Affective Disorders.

"The illness is more complicated, and then by definition how you would conceptualize how best to individualize treatment is more complicated," study co-author Dr. Mark Frye, a psychiatrist and chairman of the psychiatry/psychology department at the Mayo Clinic in Rochester, Minn., said in a Mayo news release.

"It really underscores the importance of trying to stabilize mood, because we know when people are symptomatic of their bipolar illness their binge frequency is likely to increase," Frye said. "We want to work with treatments that can be helpful but not have weight gain as a significant side effect."

The investigators plan further research to determine whether there is a genetic link between binge eating and bipolar disease.

"Patients with bipolar disorder and binge eating disorder appear to represent a more severely ill population of bipolar patients," study co-author Dr. Susan McElroy, chief research officer at the Lindner Center of HOPE, in Cincinnati, said in the news release.

"Identification of this subgroup of patients will help determine the underlying causes of bipolar disorder and lead to more effective and personalized treatments," McElroy said.